1. Field of the Invention
The present invention relates to a contact charger and image forming apparatus provided with same, such as electrophotographic copying machines, printers, facsimile and the like.
2. Description of the Related Art
In image forming apparatus such as electrophotographic copiers, printers, facsimiles and the like, the surface of an electrostatic latent image carrying member such as a photosensitive drum or the like is charged by means of a charging device. The charged region of said surface is subjected to image light exposure to form an electrostatic latent image thereon, said latent image is subsequently developed so as to be rendered visible, transferred onto a transfer medium, and fixed on said transfer medium.
Various types of such charging devices are known. Examples of such charging devices include corona chargers which utilize a corona discharge via a corotron system, scorotron system, serrated electrode array system or the like, and contact chargers wherein a charging member such as a roller, brush, film, belt or the like is brought into contact with the surface of the electrostatic latent image carrying member.
Chargers that utilize a corona discharge are advantageous insofar as they provide stabilized charging, however they also have certain disadvantages in that they produce large amounts of ozone, which leads to deterioration of the electrostatic latent image carrying member, and adversely affects humans. Thus, attention has become focused on contact chargers which produce markedly less ozone compared to corona chargers. Among the aforesaid charger types, contact chargers having a film configuration are an inexpensive charging method wherein excellent contact is readily maintainable with an electrostatic latent image carrying member.
The aforesaid contact charger of a film type provides a processing speed (peripheral speed of the electrostatic latent image carrying member) in the low range. Image forming apparatus having the processing speed in the high speed range are desirable to reduce the amount of generated ozone, however, film-type contact chargers suitable for image forming apparatus having processing speeds of 22 cm/sec or greater are not available. In other words, film-type contact chargers having a high degree of durability are not available.
In conventional film-type contact chargers, soiling of the electrostatic latent image formed on the film surface after a few image formations, e.g., soiling via adhesion of toner, paper debris and the like, produces streak-like image noise.
U.S. patent application Ser. No. 5,192,974, for example, discloses a film-type contact charger wherein the film is supported by a lateral support member, but this device does not eliminate the disadvantage of marked soiling of a stationary film. U.S. patent application Ser. No. 4,380,384 discloses a contact charger of a belt-type wherein said belt has a movable surface, but this device does not eliminate the aforesaid disadvantage because when toner once adheres to a portion of the aforesaid continuous belt, the resulting soiling of the belt surface rapidly produces a broad streak.